1. Field of the Invention
The invention relates to a mixer for mixing or blending particulate solids in the dry state or with liquid addition.
2. Description of the Prior Art
Conventional mixing machines for mixing or blending particulate solids have taken various forms and have utilized various mechanical apparatuses to affect co-mingling of ingredients placed therein. The term mixing, however, has recently come to infer that a certain relationship by volume of each of the ingredients of the total mixer charge also exists in random samples taken from the mixed product batch. Since none of the prior art of mixers have been able to provide absolute perfection, most users of such equipment have adopted standards to express the accuracy of their specific mixing machines. Such standards usually utilize statistical formulae. In a similar manner, the requirements of todays mixing machines have been dictated with respect to the power consumed by the mixing operation.
Thus, the problem areas of the prior art mixers are the speed and accuracy of mixing and the power requirements.
Some of the known mixers use to rotatable shafts with paddles or helical ribbons, as disclosed by U.S. Pat. Nos. 4,036,477; 4,278,355; 5,083,506; 4,941,132; and U.K. Patent No. 2,039,764A which are discussed subsequently. Reference also is made to German Patent Nos. 1,116,196; 1,097,411; 1,112,968; 1,045,372; 1,816,674; U.S. Patent Nos. 3,941,357 and 2,498,237.
U.S. Pat. No. 4,036,477. This machine utilizes both paddles and ribbons, however, ribbon 42 is utilized to induce discharge of material from the mixing machine. It also transfers product from one mixing tub to the other, as do paddles 36, 39 & 41. Mixing in the apparatus is accomplished by the use of paddles pitched to provide induced flow of the material from one tub to the other.
U.S. Pat. No. 4,278,355. This machine uses no ribbons, only paddles for mixing purposes. It also utilizes paddles to transfer product from one tub to the other, although the mixing technique is different from that of the machine of the '477 patent. The machine of the '355 patent creates a "fluidized" area in which the, the claim is made, rapid and gentle mixing takes place when the shaft rotation is controlled within certain specific ranges of revolutions unit time (expressed as peripheral speed). The paddles 13 of this patent are not pitched but are flat in that they are parallel with the axis of the shaft so that maximum transport of product can be achieved. Thus increases the power required for mixing.
U.S. Pat. No. 5,083,506. The device of this patent utilizes a single course of helical ribbons for each of the two shafts. It relies on timely reversing of rotational direction to obtain retention in the machine so that adequate mixing can occur. In addition, the machine has jackets on the tub(s) through which steam or other heat inducing media is pumped. Further the machine is compartmented so as to allow for variance of temperature requirements in each compartment.
U.S. Pat. No. 4,941,132. The machine of this patent uses a single helical ribbon mounted on each of two opposing shafts so arranged that product being mixed moves in opposite direction within the tub housing. The directions of rotation of the shafts are periodically reversed.
U.K. Patent No. 2,039,764. The machine of this patent has helical ribbons which vary in width or pitch. It uses flat paddles to transfer product from one mixing area to another, along with a form of a helical ribbon placed downstream from the paddle itself clearly intended as its only purpose to move product from one mixing area to the other.